Gwynne became an actress in her mid-twenties, in her first prominent television role as feminist lecturer Dr. Robyn Penrose in the BBC television mini-series dramatisation of David Lodge'sNice Work in 1989.[5]

Her first high profile comedy role was as Alex Pates in Drop the Dead Donkey in 1990. She then appeared in the 1991 Children's ITV science-fiction series Time Riders and later became a regular in Peak Practice; first appearing at the start of series 7 (Episode 1) in 1999 as Dr Joanna Graham. The character of Dr Joanna Graham was written out of the show at the end of series 9 (Episode 13) when she was fatally shot whilst intervening in a conflict between a man and his daughter. After Peak Practice Gwynne went on to star in Merseybeat in 2001.

In 2002, she starred in the TV drama for the BBCThe Secret playing the character of Emma Faraday.

She has guest starred in an episode of Lewis in the first of a new series (2008). She appeared in the first episode of series 2, "And the Moonbeams Kiss the Sea", playing the character of Sandra Walters.[9][10] She appeared in the 2011 film Hunky Dory which also stars Minnie Driver and was filmed around Swansea, Wales.[11]

In January 2014, she appeared in the episode "Fraternity" of the BBC forensic science series Silent Witness,[18]followed by appearances in another two BBC series in February: the British sitcom Uncle and the crime comedy-drama Death in Paradise (Series 3, Episode 5). [19] She recently appeared in Father Brown.